How to Modify ATX PSU to be always on

[fitzsteve]

Hi All!

I'm setting up my GREX PCI and there is some kind of fault (the ATX switch does not switch on the PSU when I press the case button) Not even if I hold it down...

I can use it with my Amigakit PSU that is 'always on'

I want to know how can I modify a normal ATX PSU to be 'always on' ?

Is it easy?

Thanks in advance

 

[sneeker]

Short the green wire to any of the black (earth) wires, leave it permanently wire them together for it to always be on.

Pin out here - http://pinouts.ru/Power/atxpower_pinout.shtml

Then you would have to turn it off with the switch on the psu.

 

[fitzsteve]

Short the green wire to any of the black (earth) wires, leave it permanently wire them together for it to always be on.

Pin out here - http://pinouts.ru/Power/atxpower_pinout.shtml

Then you would have to turn it off with the switch on the psu.

That's exactly what I want to do, that simple eh?

Wont explode in my face and destroy a BPPC?

 

[roy_bates]

Short the green wire to any of the black (earth) wires, leave it permanently wire them together for it to always be on.

Pin out here - http://pinouts.ru/Power/atxpower_pinout.shtml

Then you would have to turn it off with the switch on the psu.

That's exactly what I want to do, that simple eh?

Wont explode in my face and destroy a BPPC?

you can try to power it up without it being plugged into anything.

 

[sneeker]

No warranties express or implied.. but ive done it quite a few times in the past to see if a psu works. so you can try it without it plugged into the machine

 

[roy_bates]

just make sure its not a silent one(i think its called)i had one the once that dont power up if you short the green wire to ground.

 

[ratfink]

but you shouldn't run it for long without a load i believe.

 

[roy_bates]

but you shouldn't run it for long without a load i believe.

yeah,but youll know near enough straight away because the fan will come on.

 

[fitzsteve]

Thanks guys

If I'm offline from tomorrow onwards you no why

 

[Amigafanboi]

So what happens when you press and hold the power button on a PC?

 

[fitzsteve]

So what happens when you press and hold the power button on a PC?

veractor:

:explode

 

[sneeker]

I sends a signal to the pc motherboard, which then does the electrical equivalent of shorting the two pins together. The motherboard controls the psu in a modern pc.

 

[jvdbossc]

I have one atx psu which works and is always on with any amiga using the mod mentioned earlier. It even works without any load.. :blased:

Though mileage might vary depending on psu design. If problems arise fit some car bulbs and see.

You can also use a power resistor on the 5V line or the 3.3V line, depending on psu design. It is a waste of energy, but it might be needed. Therfore I tried many psu to avoid wasting energy using bulb(s)/resistor(s)

In modern pc 3.3V is king not 5V.

But like an 68040 is an effective way in using the 5V line..

 

[bdb]

Either put a switch from the green wire to a ground/black or turn it off by unplugging it.

I see no reason why a PSU can't be run without a load, it just wastes electricity -- the transformers are a closed circuit.

 

[AppleIIGuy]

When testing a ATX PSU I have a old Non Working SCSI HD plugged into a molex to provide a load (It does spin but nothing else)

 

[ratfink]

according to wikipedia if you don't provide the minimum specified load the psu might shut down, output incorrect voltages or otherwise malfunction. but it won't be damaged.

of course, you may know more or better, and i don't profess to know anything about this

but having said all that, seems like it's only an issue if you want to use it below the minimum specified load.

the context i'd been told this originally was in using an atx psu as a bench power supply so i guess if you are just playing with a few little components you can't necessarily rely on th voltages supplied by an atx psu being used solely for that purpose [subjecto to what these minimum requirments are - i've never noticed any and cba to look them up right now ]

 

[roy_bates]

in laymans terms the idea of shorting the green wire to the black wire is to fool the psu into thinking the psu's green wire has been sent signal low.

thats why when you turn on the atx supply theres one wire(purple i think)that sends a constant 5 volts(even when you think its off on the case) for the flip flop circuit on the mother board thats wired to the little clicky button on the case.

if you was clever enough you could make the little circiut thats does this task and wire it to the switch(temporary make switch)on the tower case,and viola power.

 

[protek]

When I powered my A590 from an ATX, it was constantly resetting itself. No such behavior, when I got an original PSU.

Ian Stedman, I think, used to make this adapter that you connect to the 24-pin molex of the ATX. It has a separate soft power switch and outputs where you can connect an A500 power cord. I've got such an adapter. Stashed, somewhere...

 

[roy_bates]

When I powered my A590 from an ATX, it was constantly resetting itself. No such behavior, when I got an original PSU.

Ian Stedman, I think, used to make this adapter that you connect to the 24-pin molex of the ATX. It has a separate soft power switch and outputs where you can connect an A500 power cord. I've got such an adapter. Stashed, somewhere...

thats the name of the supply i was thinking of that steve may have trouble with,there called "soft start supplies".

 

[fitzsteve]

Thanks guys, I soldered the wires together and covered with some heat shrink tube for a tidy finish, just tested & works great.

Yet to build the Amiga but the PSU is switching on so I'm sure it'll be fine.

It's the same PSU Amigakit use, it works just fine for Amiga's even when not under much load